Two lookup fields to same entity mapping both

On the case form, I have two different lookup fields to the sales order entity. One is called Original Sales Order and the other is called New Sales Order. They are two different relationships.

However, when I go to the sales order and create a new case from that sales order, the Original Sales Order field AND the New Sales Order field are both populated. Only the Original Sales Order field should be populated. 

From the Sales Order navigation, there are two case entities shown. Which is correct. No matter where you create the case from though both fields populate on the order.

I went into the mapping for the Original Sales Order to Case relationship and it also shows mapping for the New Sales Order link. I tried to delete this mapping but it would not allow me to. 

How do I fix this?